Fluorine-containing polymers are widely used in the fields of automobile industry, semiconductor industry and chemical industry because of their superior chemical resistance, solvent resistance and heat resistance.
However, with advances in technologies, more rigorous demand for characteristics has been imposed, and in the fields of aviation and space industries, semiconductor manufacturing equipment, chemical plant and automobile industry, more excellent heat resistance, chemical resistance, solvent resistance and processability are demanded.
In order to improve these various properties, fluorine-containing polymers having crosslinkable functional group introduced at an end thereof have been developed, and a method of introducing crosslinkable functional group easily efficiently is desired.
For example, JP2005-307026A discloses functional fluorine-containing polymer material having sulfonic acid group at an end of a graft chain in a fluorine-containing polymer. In this fluorine-containing polymer material, a resin comprising 5% by mole of trifluorobromoethylene in polytetrafluoroethylene is used, and the amount of sulfonic acid group introduced is about 0.5 meq/g. Accordingly, since reactivity is not good and many functional end groups cannot be introduced, the proposed method has a disadvantage that conversion of Rf-X to sulfonic acid is not necessarily easy.
In Prog. Polymn. Sci., 1989, 14, 251-296 and JP2002-514242A, a method of initiating polymerization with persulfates such as ammonium persulfate and potassium persulfate is described. These documents describes that in free radical polymerization thermally initiating polymerization by using a reducing agent such as sodium sulfite or sodium hydrogensulfite and persulfate, a polymer having both of carboxylic acid end group and sulfonic acid end group is prepared. In the case of this method, polymers having the same functional end groups cannot be obtained, and accordingly, since reactivity of end groups is different, the use as an intermediate of a polymer is difficult.
Further, also introduction of sulfinic acid group in low molecular weight compounds is described in JP11-509244A and Tetrahedron Lett., 1998, 39, 8487-8490. This reaction is carried out under heating in the presence of a basic substance. However, under these conditions, release of fluorine atom from vinylidene fluoride polymer chain occurs, and therefore, the reaction cannot be applied to high molecular reaction of vinylidene fluoride polymer.